1. Field of the Invention
The present invention relates to a rubber part having a metal fitting such as a bushing and an engine mount for automobiles, and a vibration damping member for industrial machineries, and a method of producing the same.
2. Description of the Art
Generally, bushings and engine mounts for automobiles, and vibration damping members for industrial machineries consist of a rubber part having a metal fitting, which is formed by integrating the metal fitting and the rubber part and is used as a connecting member between various components of a frame or an engine.
The rubber part having a metal fitting has a problem that corrosion on a surface of the metal fitting on an interface between the rubber part and the metal fitting causes separation therebetween, leading to a deterioration of the function of the rubber part having a metal fitting. For preventing the corrosion, the surface of the metal fitting is generally subjected to chromate treatment to form a chromate-based chemical film on the surface as disclosed in, for example, Japanese Unexamined Patent Publication No. 6-179978.
However, the chromate treatment has a problem that chemical conversion treatment liquids used for the treatment include hexavalent chromium which causes damage on human bodies and environments.
Further, since crystallization water contained within the film structure of the chromate-based chemical film is easily dehydrated by heat generated during vulcanization of rubber, the film is vulnerable to cracks because of contraction of film and to deterioration of adhesiveness. If a metal fitting under this condition is processed for diameter reduction or the like, the film may be unable to transform following the squeeze of the metal fitting, and cracks may be formed in the film, which leads to insufficient protection against corrosion.
In view of the foregoing, it is an object of the present invention to provide a rubber part having a metal fitting provided with an anti-corrosion chemical film formed on the surface of the metal fitting, which is harmless to human bodies and environments and is capable of transforming following the squeeze of the metal fitting.